This invention relates in general to electrotherapy apparatus and, more specifically to an interferential generator for treating a living body with low frequency therapeutic current at a selected point.
A wide variety of transcutaneous electrical nerve stimulation (TENS) devices have been developed to deliver electrical current to an area of a living body, typically a human being, to alleviate pain. Typical of these is U.S. Pat. No. 4,989,605 to Rossen, which applies a carrier signal to the skin through an electrode. The signal is in the form of D.C. bursts in the frequency range of 10,000 to 19,000Hz which is modulated on and off at a lower frequency. Other typical TENS type devices include the microprocessor controlled device for applying a low frequency pulse train and a modulated high frequency pulse train to a patient through an electrode as disclosed by Padjen et al in U.S. Pat. No. 4,719,922, a device in which a constant current square wave signal is directed into the body between two electrodes as described by Hudleson et al in U.S. Pat. 4,232,680 and a device in which a high frequency low amperage current is applied to a body through an electrode as described by Liss et al in U.S. Pat. No. 3,902,502.
The prior art TENS devices deliver a wide area stimulation, rather than the generally preferable localized stimulation. Also, prior art devices tend to provide a uniform signal throughout a treatment. The body tends to accommodate to the stimulation, lessening its effectiveness over time. While of varying effectiveness, the prior devices are not as effective as would be desired in treating pain and other conditions. Thus, there is a continuing need for electrotherapy devices of improved effectiveness.